Delivery pump for a fluid, metering device having the delivery pump and motor vehicle having the metering device

ABSTRACT

A delivery pump for delivering a fluid includes a delivery piston to be moved in a delivery direction from a pump inlet to a pump outlet. The delivery piston is supported in an axial bearing having a cooling device for cooling the axial bearing with the fluid. A metering device having the delivery pump and a motor vehicle having the metering device are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of EuropeanPatent Application EP 11 290 490.9, filed Oct. 21, 2011; the priorapplication is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a delivery pump for a fluid, which can be usedin a metering device, for example, to meter a fluid from a tank into anexhaust gas treatment device for cleaning exhaust gases from an internalcombustion engine. The invention also relates to a metering devicehaving the delivery pump and a motor vehicle having the metering device.

Exhaust gas treatment devices in which a fluid is fed in for the purposeof cleaning the exhaust gases are widely used, especially in the motorvehicle sector.

One exhaust gas cleaning method, which is carried out particularly oftenin such exhaust gas treatment devices, is that of the selectivecatalytic reduction or SCR method, in which nitrogen oxide compounds inthe exhaust gas are reduced through the use of a reducing agent. Ammoniais generally used as the reducing agent in that case. In motor vehicles,ammonia is normally not stored in the pure form but in the form of aprecursor solution or precursor fluid, which can be converted intoammonia.

An aqueous urea solution is used, for example, as the precursorsolution. A 32.5% aqueous urea solution, which can be obtained under thetrademark AdBlue®, is used particularly often.

That precursor solution can then be fed in to the exhaust gas in liquidform and then converted into ammonia in the exhaust gas by purelythermal measures or by hydrolytic measures with support from ahydrolysis catalytic converter. It is also possible for the precursorsolution to be converted to ammonia outside the exhaust gas in a reactorprovided for that purpose.

A delivery pump is normally required in order to deliver the solutionfrom a tank to the exhaust gas treatment device or to a reactor. Thedelivery pump must make the reducing agent available to the exhaust gastreatment device during the entire period of operation of a motorvehicle. The delivery pump must therefore have a very long service life.Moreover, the delivery pump should be as inexpensive as possible.

A delivery pump for reducing agent is known, for example, from GermanPatent DE 10 2008 010 073 B4.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a delivery pumpfor a fluid, a metering device having the delivery pump and a motorvehicle having the metering device, which overcome thehereinafore-mentioned disadvantages and further mitigate the technicalproblems of the heretofore-known pumps, devices and vehicles of thisgeneral type. In particular, the intention is to describe a furtherimproved, particularly advantageous delivery pump for a fluid which issuitable especially for delivering reducing agent.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a delivery pump for delivering a fluid.The delivery pump comprises a pump inlet and a pump outlet defining adelivery direction therebetween. A delivery piston is configured to movein the delivery direction from the pump inlet to the pump outlet. Anaxial bearing supports the delivery piston therein. A cooling device isassociated with the axial bearing and configured to cool the axialbearing with the fluid.

The delivery pump is suitable especially for delivering reducing agentand, in particular, aqueous ammonia solution as a fluid.

The delivery pump is preferably suitable for making the fluid availableat a defined pressure at the pump outlet or for achieving a definedincrease in the pressure of the fluid from the pump inlet to the pumpoutlet. For this purpose, a delivery pump drive can be controlled by acontrol unit, in which the control unit receives information from atleast one pressure sensor for the purpose of adjusting the definedpressure or the defined increase in pressure. The control unit cancontrol the delivery pump drive on the basis of information from atleast one pressure sensor. The delivery pump drive is preferably a drivecoil. When an electric current flows through the drive coil, the drivecoil produces an electromagnetic force which acts on the delivery pistonof the delivery pump. The delivery piston can be set in motion by theforce of the drive coil. The drive can also have a spring which canexert a restoring force on the delivery piston. By way of example, adrive coil can be set up to move the delivery piston towards the pumpoutlet in the delivery direction, counter to a spring, when a currentflows through the drive coil. The spring can be set up to return thedelivery piston towards the pump inlet, counter to the deliverydirection, when no current is flowing through the drive coil and thedrive coil is therefore not exerting any force on the delivery piston.

The pump inlet is preferably constructed for the connection of an intakeline, through which the delivery pump can draw in fluid from a tank, forexample. The pump outlet is preferably constructed for the connection ofa pressure line, into which the delivery pump can deliver fluid, e.g.towards an exhaust gas treatment device or towards an injector whichopens into an exhaust gas treatment device. In order to connect theintake line and the pressure line, the pump inlet and the pump outletpreferably have corresponding connectors, to which the lines can bedetachably connected. The delivery piston is preferably disposed on acommon axis together with the pump inlet and the pump outlet.

The axial bearing preferably allows movement of the delivery piston onlyin an axial direction extending along the delivery direction from thepump inlet to the pump outlet. Rotation or translational displacement ofthe delivery piston is preferably prevented by the axial bearing. Theaxial bearing is preferably a plain or slide bearing. The deliverypiston has a piston surface, and the axial bearing has a guidingsurface. The piston surface and the guiding surface can slide upon oneanother.

Details of the construction of such a delivery pump may be obtained inthis case by making reference especially to German Patent DE 10 2008 010073 B4, which illustrates the construction thereof in detail in FIG. 2and provides explanations pertaining thereto in paragraphs [0039] to[0045]. FIG. 2 and the paragraphs thereof mentioned above are herebyincorporated herein in full by reference.

As the piston surface and the guiding surface slide upon one another inthe axial bearing, heat is generated by friction. The cooling device ispreferably set up to deliver the fluid into the axial bearing andpreferably to the piston surface and the guiding surface in order toabsorb and, where appropriate, carry away heat from the axial bearing.It has been found that high temperatures in the axial bearing of adelivery pump can drastically shorten the life of the delivery pump.This is the case especially when the delivery pump is used to deliveraqueous urea solution. At high temperatures, urea precipitates may formin the aqueous urea solution. Those precipitates act like abrasiveparticles in the delivery pump and especially in a plain bearing and candamage the bearing and the delivery pump. It is therefore advantageous,especially for delivery pumps for delivering aqueous urea solution, tocarry away the heat produced in a plain bearing. It is particularlyadvantageous for this purpose to use the fluid which is alreadyavailable in the delivery pump.

In accordance with another particularly advantageous feature of theinvention, the cooling device is simultaneously a lubricating device forlubricating the axial bearing with the fluid.

An axial bearing which is embodied as a plain bearing is generallyadvantageous if a lubricant is provided. The lubricant reduces thefriction between the surfaces in the plain bearing. In the deliverypumps considered herein, the surfaces of the plain bearing arepreferably a piston surface of the delivery piston and a guiding surfaceof a guide bore of the axial bearing in which the piston is guided. Itis particularly preferred if a gap, in which a lubricating film formedof the fluid is formed, is provided between the piston surface and theguiding surface.

By virtue of the fact that the fluid is simultaneously used as a coolantand a lubricant for the axial bearing of the delivery pump, it may bepossible to dispense with an additional lubricant for the axial bearing.

In accordance with a further particularly advantageous feature of theinvention, the axial bearing is a guide channel, in which the deliverypiston is supported in a sliding manner, and the cooling device isembodied as at least one passage, which intersects the guide channel andthrough which the fluid enters the guide channel at least at one entrypoint.

The shape of the guide channel is preferably matched to a cross sectionof the delivery piston to enable the delivery piston to be movedbackwards and forwards in the guide channel in a delivery movement. Thepassage can be a bore, a gap or a slot, for example, which meets theguide channel and thus intersects the guide channel.

A plurality of passages is preferably disposed along the guide channelto enable the axial bearing or guide channel or guiding surface and thepiston surface to be wetted as fully as possible with fluid. As anotherpreferred option, a plurality of passages is also disposed around thedelivery piston and the guiding channel in the circumferential directionto ensure complete wetting. For example, two to eight passages leadingto the guide channel and distributed uniformly in the circumferentialdirection are in each case provided in two to six planes along the guidechannel.

The passages can be embodied as bores, gaps or the like, for example.The passages establish a connection through which the fluid can passinto the axial bearing or guide channel. This connection preferablyextends from a channel through the delivery pump through which the fluidpasses on the way from the pump inlet to the pump outlet or along whichchannel the fluid flows during normal delivery.

The passages described herein are a technically particularlyuncomplicated and effective configuration for passing the fluid into theaxial bearing.

In accordance with an added particularly advantageous feature of theinvention, the delivery piston has at least one recess in the region ofthe passage. The recess crosses the entry point of the passage during adelivery movement of the delivery piston in the axial bearing and, inthe process, delivers the fluid into the axial bearing.

The delivery piston preferably has a largely flat piston surface matchedto the shape or guiding surface of the guide channel. Both the pistonsurface and the guiding surface preferably have a low roughness of, forexample, less than 10 μm [micrometers] and preferably even less than 5μm [micrometers]. The roughness of these surfaces is low in order toreduce the friction of the delivery piston in the guide channel of theaxial bearing. The recess forms a re-entrant area of the delivery pistonrelative to the piston surface. The recess can be embodied as a singlenotch or opening in the delivery piston. It is also possible for therecess to form a complete network or complete system of channels on thepiston surface, through which the fluid can pass, and thus allowdistribution of the fluid over the piston surface and over the guidingsurface. When the recess crosses the passage, an area of the recess andan area of the entry point of the passage overlap at least partially inan overlap zone. The fluid can then enter the recess from the passage.The delivery movement changes the area of the overlap zone because theentry point and the recess move relative to one another. During thedelivery movement, there is preferably at least at times no overlap atall between the area of the entry point and the area of the recess.Indeed, the recess preferably crosses several different passages duringthe delivery movement. The fluid pressures prevailing at these differentpassages are preferably different. The fluid can thus be deliveredeffectively through the axial bearing by the recess.

The use of at least one recess in the delivery piston for delivering thefluid into the axial bearing is particularly advantageous because thefluid is delivered effectively into the axial bearing and there is noneed for any additional moving parts (such as an additional pump) fordelivering the fluid into the axial bearing.

In accordance with an additional particularly advantageous feature ofthe invention, the axial bearing is embodied with a gap between aguiding surface of a guide channel of the axial bearing and a pistonsurface of the delivery piston, in which the gap has a gap width of atleast 5 μm [micrometers].

Such a gap width between the piston surface and the guiding surface isparticularly advantageous in ensuring that a film of the fluid forms inthe axial bearing or guide channel or gap, with this film beingparticularly advantageous for cooling and, where appropriate, also forlubricating the axial bearing.

In accordance with yet another particularly advantageous feature of theinvention, the axial bearing is set up in such a way that a backflow offluid through the axial bearing counter to the delivery direction of thedelivery pump is obtained.

The backflow preferably covers the entire length of the axial bearing.In this way, particularly effective cooling of the axial bearing can beachieved. It also ensures that cooling of the axial bearing is uniformlydistributed over the entire length of the axial bearing and also that nolocal overheating of the axial bearing occurs.

In accordance with yet a further particularly advantageous feature ofthe invention, the delivery pump has a delivery chamber, at least onechamber inlet opening, which opens into the delivery chamber, and atleast one nonreturn valve, which is disposed between the deliverychamber and the pump outlet in the delivery direction, wherein thedelivery piston can perform a delivery movement into the deliverychamber and, in the process, pushes fluid present in the deliverychamber out through the nonreturn valve in the delivery direction to thepump outlet.

During the delivery movement, the delivery piston moves into and out ofthe delivery chamber in a regular manner. During the delivery movementof the delivery piston, the volume of the delivery chamber is thusincreased and reduced in a regular manner. In a particularlyadvantageous variant of the delivery pump, the reduction in the volumeis such that the minimum volume of the delivery chamber which occursduring the delivery movement is at least ten times, preferably twentytimes, and particularly preferably one hundred times, less than themaximum volume of the delivery chamber which occurs. Fluid can enter thedelivery chamber in the delivery direction through at least one chamberinlet opening which opens into the delivery chamber. If a plurality ofchamber inlet openings is provided, they are preferably all located in acommon plane aligned perpendicularly to the direction of movement or tothe axis of movement of the delivery piston. This is possibleparticularly if the delivery piston is disposed close to a position ofmaximum retraction (that is to say in a direction towards the pumpinlet) during the delivery movement and, in this case, the volume of thedelivery chamber is close to the maximum volume described. During thedelivery movement, the delivery piston preferably passes over the atleast one chamber inlet opening. When the delivery piston is coveringthe chamber inlet opening, no fluid can flow into the delivery chamber.When the delivery piston opens the delivery chamber, fluid can flow intothe delivery chamber through the chamber inlet opening. There is anonreturn valve between the delivery chamber and the pump outlet in thedelivery direction. During a part of the delivery movement in thedirection towards the pump outlet, the delivery piston pushes fluid outof the delivery chamber, through the nonreturn valve, towards the pumpoutlet. The nonreturn valve prevents fluid from flowing back into thedelivery chamber from the pump outlet.

Through the use of a delivery pump constructed in this way, it is alsopossible to achieve a delivery pump with a relatively high meteringaccuracy. The delivery pump can then be used not only as a simpledelivery pump but also as a metering pump. In the case of a meteringpump, the quantity of fluid delivered by the delivery pump can bedetermined precisely. In the case of the delivery pump described herein,the quantity of fluid delivered is obtained from the number of deliverystrokes of the delivery piston and the delivery chamber volume which thedelivery chamber has when the delivery piston is just covering thechamber inlet openings. The delivery quantity can be calculated as theproduct of this volume and the number of delivery strokes.

In order to obtain details of the construction of a delivery chamber ofa delivery pump, reference may be made in this case once againespecially to German Patent DE 10 2008 010 073 B4, which illustrates anddescribes the construction of a delivery chamber in detail in FIG. 2 andin the explanations pertaining thereto in paragraphs [0039] to [0045].FIG. 2 and the paragraphs mentioned are incorporated herein in full byreference.

With the objects of the invention in view, there is also provided ametering device for delivering a reducing agent from a tank into anexhaust gas treatment device. The metering device comprises a deliveryline leading from the tank to the exhaust gas treatment device, and adelivery pump according to the invention disposed in the delivery lineand configured to deliver reducing agent as the fluid from the tank tothe exhaust gas treatment device.

The delivery pump described, as explained above, is particularlyadvantageous for delivering reducing agent. It is therefore particularlyadvantageous to employ the delivery pump described in a metering devicefor reducing agent.

With the objects of the invention in view, there is concomitantlyprovided a motor vehicle, comprising an internal combustion engine, atank for reducing agent, an exhaust gas treatment device for cleaningexhaust gases from the internal combustion engine, and a metering deviceincluding a delivery line leading from the tank to the exhaust gastreatment device and a delivery pump according to the invention disposedin the delivery line and configured to meter the reducing agent from thetank to the exhaust gas treatment device.

Other features which are considered as characteristic for the inventionare set forth in the appended claims, noting that the features presentedindividually in the claims can be combined in any technologicallymeaningful way and can be supplemented by explanatory material from thedescription, giving rise to additional variant embodiments of theinvention.

Although the invention is illustrated and described herein as embodiedin a delivery pump for a fluid, a metering device having the deliverypump and a motor vehicle having the metering device, it is neverthelessnot intended to be limited to the details shown, since variousmodifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, longitudinal-sectional view of a variantembodiment of a delivery pump; and

FIG. 2 is a vertical-sectional view of a motor vehicle having a meteringdevice with a delivery pump.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first,particularly, to FIG. 1 thereof, there is seen a delivery pump 1 whichcan deliver a fluid from a pump inlet 3 to a pump outlet 4 in a deliverydirection 5. In order to deliver the fluid, the delivery pump 1 has adelivery piston 2, which can be moved back and forth in an axial bearing6. During this movement in the axial bearing 6, the delivery piston 2performs a delivery movement 11. During the delivery movement 11, thedelivery piston 2 moves into and out of a delivery chamber 18 in aregular manner. During the delivery movement 11 of the delivery piston2, the volume of the delivery chamber 18 is increased and reduced in aregular manner. In a particularly advantageous variant of the deliverypump 1, the reduction in the volume is such that a minimum volume of thedelivery chamber 18 which occurs during the delivery movement 11 is atleast ten times, preferably twenty times, and particularly preferablyone hundred times, less than the maximum volume of the delivery chamber18 which occurs. Fluid can enter the delivery chamber 18 in the deliverydirection 5 through at least one chamber inlet opening 19 opening intothe delivery chamber 18. This is possible particularly if the deliverypiston 2 is disposed close to a position of maximum retraction (that isto say in a direction towards the pump inlet 3) during the deliverymovement 11 and, in this case, the volume of the delivery chamber 18 isclose to the maximum volume described. During the delivery movement 11,the delivery piston 2 preferably passes over the at least one chamberinlet opening 19. When the delivery piston 2 is covering the chamberinlet opening 19, no fluid can flow into the delivery chamber 18. Whenthe delivery piston 2 opens the delivery chamber 18, fluid can flow intothe delivery chamber 18 through the chamber inlet opening 19. There is anonreturn valve 20 between the delivery chamber 18 and the pump outlet 4in the delivery direction 5. During a part of the delivery movement 11in the direction towards the pump outlet 4, the delivery piston 2 pushesfluid out of the delivery chamber 18, through the nonreturn valve 20,towards the pump outlet 4. The nonreturn valve 20 prevents fluid fromflowing back into the delivery chamber 18 from the pump outlet 4. Thedelivery movement 11 of the delivery piston 2 is achieved at least inpart through the use of a drive coil 27. An electric current can bepassed through the drive coil 27. The drive coil 27 then exerts anelectromagnetic force on the delivery piston 2, and the delivery piston2 is moved. In addition, a non-illustrated spring can also be providedon the delivery piston 2, exerting a restoring force on the deliverypiston 2 acting counter to a direction of action of the drive coil 27,for example.

The axial bearing 6 of the delivery piston 2 is preferably embodied inthe manner of a plain bearing. The axial bearing 6 is constructed as aguide channel 8, in which the delivery piston 2 lies. The guide channel8 has a guiding surface 14, and the delivery piston 2 has a pistonsurface 15. The guiding surface 14 and the piston surface 15 can slideupon one another, thus allowing the delivery piston 2 to perform thedelivery movement 11 in the guide channel 8 or axial bearing 6. There ispreferably a gap 13 between the piston surface 15 and the guidingsurface 14. The gap has a gap width 16 of at least 5 μm [micrometers],for example, to enable the piston surface 15 to slide easily on theguiding surface 14.

The axial bearing 6 has a cooling device 7. The cooling device 7 isconstructed to deliver the fluid delivered by the delivery pump 1 intothe axial bearing 6 and especially into the gap 13 between the pistonsurface 15 and the guiding surface 14. In the variant embodimentillustrated herein, the cooling device 7 is at least one passage 9,through which the fluid can enter the axial bearing 6 or guide channel 8or gap 13. For this purpose, the passage 9 intersects the guide channel8. The passage 9 opens into the axial bearing or guide channel 8 at anentry point 12. The passage 9 is constructed as a bore, notch or slot inthe wall of the guide channel 8, for example, and preferably forms aconnection through which the fluid can pass into the axial bearing 6 orguide channel 8 or gap 13.

At least one recess 10 is preferably provided in the delivery piston 2.The recess 10 is disposed in such a way that it passes over the entrypoint 12 of the passage 9 when the delivery piston 2 performs thedelivery movement 11. The recess 10 thus promotes and intensifies thedelivery of fluid into the axial bearing 6 or guide channel 8 or gap 13.A backflow 17 of fluid through the axial bearing 6 or guide channel 8 orgap 13 counter to the delivery direction 5 is preferably established.

FIG. 2 shows a motor vehicle 25 having an internal combustion engine 26and an exhaust gas treatment device 23 for cleaning the exhaust gases ofthe internal combustion engine 26. The reducing agent can be deliveredfrom a tank 22 for a reducing agent into the exhaust gas treatmentdevice 23 through the use of a metering device 21. The metering device21 furthermore has a delivery line 24 from the tank 22 to the exhaustgas treatment device 23. A delivery pump 1 for delivering the reducingagent is provided in the delivery line 24.

1. A delivery pump for delivering a fluid, the delivery pump comprising:a pump inlet and a pump outlet defining a delivery directiontherebetween; a delivery piston configured to move in said deliverydirection from said pump inlet to said pump outlet; an axial bearingsupporting said delivery piston therein; and a cooling device associatedwith said axial bearing and configured to cool said axial bearing withthe fluid.
 2. The delivery pump according to claim 1, wherein saidcooling device is also a lubricating device configured to lubricate saidaxial bearing with the fluid.
 3. The delivery pump according to claim 1,wherein: said axial bearing is a guide channel configured to supportsaid delivery piston therein in a sliding manner; and said coolingdevice is constructed as at least one passage intersecting said guidechannel and directing the fluid to enter said guide channel through saidat least one passage at least at one entry point of said at least onepassage.
 4. The delivery pump according to claim 3, wherein saiddelivery piston has at least one recess in vicinity of said at least onepassage, said at least one recess crossing said entry point of said atleast one passage during a delivery movement of said delivery piston insaid axial bearing while delivering the fluid into said axial bearing.5. The delivery pump according to claim 1, wherein: said guide channelof said axial bearing has a guiding surface; said delivery piston has apiston surface; and said axial bearing is formed with a gap between saidguiding surface and said piston surface, said gap having a gap width ofat least 5 pm [micrometers].
 6. The delivery pump according to claim 1,wherein said axial bearing is configured to produce a backflow of fluidthrough said axial bearing counter to said delivery direction.
 7. Thedelivery pump according to claim 1, which further comprises: a deliverychamber having at least one chamber inlet opening opening into saiddelivery chamber; and at least one nonreturn valve disposed between saiddelivery chamber and said pump outlet in said delivery direction; saiddelivery piston configured to perform a delivery movement into saiddelivery chamber while pushing fluid present in said delivery chamberout through said nonreturn valve in said delivery direction to said pumpoutlet.
 8. A metering device for delivering a reducing agent from a tankinto an exhaust gas treatment device, the metering device comprising: adelivery line leading from the tank to the exhaust gas treatment device;and a delivery pump according to claim 1 disposed in said delivery lineand configured to deliver reducing agent as the fluid from the tank tothe exhaust gas treatment device.
 9. A motor vehicle, comprising: aninternal combustion engine; a tank for reducing agent; an exhaust gastreatment device for cleaning exhaust gases from said internalcombustion engine; and a metering device including a delivery lineleading from said tank to said exhaust gas treatment device and adelivery pump according to claim 1 disposed in said delivery line andconfigured to meter the reducing agent from said tank to said exhaustgas treatment device.